Rotating magnetic memories are becoming increasingly sophisticated to accomodate the growing need for reliable data storage and retrieval. So-called flexible or "floppy" disk drives are still in great demand, but there is mounting pressure to improve their performance and reliability while reducing their manufacturing cost.
As is known, floppy disk drives employ a disk-shaped, centrally apertured, compliant magnetic recording medium which conventionally is housed for rotation within a protective envelope or jacket, so that there is minimal direct contact with the recording medium as it is being inserted into and removed from the disk drive or otherwise being handled. The jacket, in turn, has several strategically located openings for exposing the recording medium, including a centrally located aperture so that the recording medium or "disk" can be centered on and clamped to a rotatably driven spindle, and at least one radially elongated slot to enable a recording head to access the disk for writing data on and reading data from anyone of a plurality of concentric tracks.
Substantial effort and expense have been devoted to designing media centering and clamping mechanisms for floppy disk drives. High performance floppy disk drives require precise centering of the recording medium with respect to the spindle to avoid unacceptable "off-track errors" and positive, non-slip clamping of the recording medium to the spindle to avoid unacceptable "bit time displacement errors" while data is being stored (i.e., "written") or retrieved (i. e., "read"). Furthermore, the disk centering and clamping action need not only be repeatable by a single disk drive, but also replicatable by other disk drives because data recorded by one disk drive is often read out by another. Indeed, one of the basic advantages of floppy disk drives is that the recording medium is removeable, whereby data may be easily "transported" from one drive to another.
Expandible collet-type disk centering and clamping mechanisms have been especially well received and are widely utilized in modern floppy disk drives. They characteristically require that the spindle have a central cylinderical bore or recess for receiving a positioning cone or collet having a generally circular arry of flexible fingers. In operation, the fingers radially expand against the inner edge of the central aperture in the recording medium while the collet is being seated within the spindle bore, thereby centering the recording medium or disk on the spindle. Examples of this type of clamping mechanism can be found in U.S. Pat. Nos. 4,125,883, 4,193,101, 4,409,629, 4,413,294 and 4,430,678. Typically, the collet is plastic and is designed so that its fingers resiliently deform whenever any force great enough to cause unwanted crimping or bending of the recording medium is applied thereto, thereby protecting the recording medium from being damaged. Furthermore, provision is usually made to ensure that little, if any, clamping pressure is applied to the recording medium until it is centered on the spindle. To that end, the clamping pressure conventionally is furnished by flanges which extend outwardly from the fingers of the collet to clamp the recording medium against an annular rim or face of the spindle only when the collet is substantially fully seated within the spindle bore.
The disk centering action of these expandible collet-type mechanisms usually is quite precise and readily repeatable. Unfortunately, however, their clamping action tends to be very sensitive to minor variations in the tilt of the collet relative to the spindle and to minor variations in the relative parallelism and flatness of the mating surfaces of the collet and spindle. Indeed, the ordinary manufacturing tolerances required to accomodate available, low cost, mass production techniques generally are sufficient to affect the clamping pressure provided by such mechanisms. Thus, the known expandible collet-type disk centering and clamping mechanisms have not fully satisfied the need for a low cost, readily replicatable clamp for repeatedly and positively clamping recording media in floppy disk drives.